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A method is proposed for calculating low interfacial tension (IFT) based on molecular dynamics simulation of systems with superdense packing of surfactant molecules at the water–liquid hydrocarbon interface. The interfacial tension was calculated by the molecular dynamics method using the all-atom and coarse-grained models in water–alkane (decane, dodecane) two-phase systems in the presence of various individual surfactants. The following ionic and nonionic surfactants were considered: sodium dodecyl sulfate (SDS), cetyltrimethylammonium chloride (CTAC), sodium dodecylbenzenesulfonate (SDBS), sodium decet-6 sulfate C10E6SO4Na, hexaethylene glycol monodecyl ether (C10E6), triethylene glycol monononadecyl ether (C19E3), and octapropoxypentaethylene glycol monododecyl ether (C12P8E5). It was shown that the interfacial tension decreases to zero when surfactant adsorption increases to the limiting values. [ABSTRACT FROM AUTHOR]

The paper investigates the process of liquid-phase sintering of amorphous iron-based nanoparticles by the method of molecular dynamics simulations. The classical molecular dynamics package LAMMPS was used for modeling. Visual analysis of the atomic configurations of nanoparticles during their rapid cooling revealed the self-purification effect of the particles. Partial pair correlation functions and coordination number distribution functions were used to analyze the atomic structure of nanoparticles after sintering. As a result of the analysis of the main structural parameters, which were obtained using the specified functions, differences in the atomic composition and structure of the volume and surface of nanoparticles were established.

Scenarios of structure formation in four-component nanoparticles are considered. The objects of study were Au-Cu-Pd-Pt nanoparticles containing N = 400, 800, 1200, 1600, 2000, 4000 atoms of the stoichiometric composition Au3CuPd12Pt4. Two alternative modeling methods were used: the molecular dynamics and the Monte Carlo. The interaction between atoms was described by the tight binding potential. The phase transition temperatures for the nanoparticles under study were determined. It has been established that the melting and crystallization temperatures depend both on the size of nanoparticles and on the rate of temperature change (by using the molecular dynamics method). The melting rate of nanoparticles has little effect on the melting temperature, while increasing the cooling rate significantly reduces the crystallization temperature and slows down the segregation processes. The process of coalescence of two four-component nanoparticles was modeled. During the process of coalescence, significant mixing of atoms of different types does not occur when using the Monte Carlo method, which leads to some stopping of the growth of the neck at the point of contact, in contrast to molecular dynamics method, where the growth of the neck occurs gradually.

The final configurations obtained during crystallization in ternary metal nanoalloys Tix-Al96-x-V4 of various compositions were studied. The molecular dynamics method was used as an atomistic simulation method. Interatomic interaction was described by the tight-binding potential. The size dependence of melting temperatures, as well as changes in melting and crystallization temperatures with changes in the composition of ternary nanoparticles, have been determined. Based on the results of a series of computer experiments, differences in the crystallization scenarios of Tix-Al96-x-V4 ternary nanoparticles were established. A classification based on internal structure and degree of crystallinity was proposed and tested. For Tix-Al96-x-V4 ternary nanoparticles, five main classes are identified based on the number of (semi) axes of 5th order symmetry. Despite the fact that studying the segregation of components of Tix-Al96-x-V4 ternary nanoparticles was not the goal of the work, atomic configurations corresponding to different temperatures during the cooling process were constructed and described.

In this work, scenarios of structure formation in ternary nanoparticles based on platinum and palladium of four stoichiometric compositions of different sizes were studied, with nickel acting as a dopant. Two alternative methods were used: the molecular dynamics method (implemented in the open source software LAMMPS) and the Monte Carlo method (implemented in the Metropolis scheme). In addition, to describe the interatomic interaction, two versions of force fields were used: the modified tight-binding potential (when implementing the molecular dynamics and Monte Carlo methods) and the embedded atom potential (when implementing the molecular dynamics method). Based on the results of a series of computer experiments, it was found that palladium atoms have increased segregation to the surface. At a cooling rate of 0,1 K/ps, an ordered crystalline FCC structure with inclusions of the HCP phase is formed. With an increase in the nickel dopant content to 20% in the ternary Pd-Pt-Ni nanoparticle, the identifiable local structure becomes more complex, both in terms of the number of phases and in terms of structural segregation.

The processes of structure formation in Co-Au and Ti-V metal nanoparticles as well as factors affecting the crystallization process are considered. The objects of the study were Co-Au and Ti-V binary nanoparticles containing N = 400, 800, 1520 and 5000 atoms with the equiatomic composition. The computer experiment was carried out using method of molecular dynamics. The interatomic interaction was described by the tight-binding potential. According to the results of a series of computer experiments, it was found that the main factors influencing the possibility of obtaining crystalline phases are: the cooling rate of binary nanoparticles, their size and the size mismatch of atoms included in the composition, as well as the nature of the interaction of metal atoms. The manifestation of stability/instability in binary nanoparticles may be due to patterns of formation of crystalline phases. Moreover, the tendency to segregate one of the components in a binary system may not be the main factor determining the stability/instability of such a system.

The melting and crystallization phase transitions in the five-component metallic Au-Ag-Cu-Pd-Pt equiatomic nanosystem were investigated. The complex approach to atomistic modeling is due to the use of alternative methods of computer simulation – the molecular dynamics and Monte Carlo methods. The interatomic interactions were described by the tight-binding potential. According to the results of a series of computer experiments, it was established that five-component nanoparticles of equiatomic composition can form crystalline phases during cooling. Melting and crystallization temperatures for the investigated five-component nanoparticles were determined. The values obtained by alternative methods are in good agreement. For five-component nanoparticles, the concept of fixing the temperatures corresponding to the beginning and end of the phase transition process is confirmed. The metals that make up five-component nanoparticles, the atoms of which in the process of crystallization form the central part of the nanoparticle (core) and the peripheral regions, including the surface of the nanoparticle, are determined.

Results on a nanoparticle impact onto a target calculated by the molecular dynamics method are presented. The first problem being solved is the nanoparticle impact onto a target under the conditions of cold gas-dynamic spraying. The second problem deals with nanoparticle extension, which adheres to the target due to the impact. It is shown that a chemical bond between the nanoparticle and target is formed during the impact. The bond in the case of the titanium nanoparticle impact onto an aluminum target is found to be stronger than that in the case of the aluminum nanoparticle impact onto a titanium target. The reason is that the titanium nanoparticle penetrates into the aluminum target to a greater depth. [ABSTRACT FROM AUTHOR]

This paper presents the results of molecular dynamic modeling, revealing that inserting confined graphene layers into copper crystal reduces the thermal conductivity of the whole composite, and the coefficient of thermal conductivity κ decreases upon an increase in the number of graphene layers. The injection of one, two, and three layers of 15 nm graphene leads to a change in the coefficient of thermal conductivity from 380 W/(m·K) down to 205.9, 179.1, and 163.6 W/(m·K), respectively. Decreasing the length of graphene layers leads to a decrease in the density of defects on which heat is dissipated. With one, two, and three layers of 8 nm graphene, the coefficient of thermal conductivity of the composite is equal to 272.6, 246.8, and 240.8 W/(m·K), appropriately. Meanwhile the introduction of an infinite graphene layer results in the growth of κ to 414.2–803.3 W/(m·K). [ABSTRACT FROM AUTHOR]

To elucidate the impact mechanism of the interfacial characteristics of Calcium Silicate Hydrate gel (CSH)–Montmorillonite (MMT) at the nanoscale on the strength of cement-stabilized montmorillonite soil, this paper begins by examining the interfacial energy. Through Molecular Dynamics (MD) simulation methods, the energy at the MMT and CSH binding interface is quantitatively calculated, and the correlation between the interfacial energy and macroscopic strength is determined in conjunction with grey relational analysis. Finally, based on the characterization results from X-ray diffraction (XRD), the accuracy and sources of deviation in the MD simulation results are discussed. The study shows the CSH-MMT interfacial energy is composed of van der Waals forces, hydrogen bond energy, and electrostatic interactions, which are influenced by the migration of cations; there is a good consistency between the CSH-MMT interfacial energy and the unconfined compressive strength (UCS) of cement-stabilized soil (cemented soil), with the interfacial energy decreasing as the number of water molecules increases and first decreasing then increasing as the number of MMT layers grows; by adjusting the mix proportions, the magnitude of the CSH-MMT interfacial energy can be altered, thereby optimizing the strength of the cemented soil. [ABSTRACT FROM AUTHOR]

This study focuses on the behavior of the Carbon Nanotube (CNT)-C20 system as a nano-pumping configuration for drug delivery processes. The system was modeled using a molecular dynamics (MD) method, and the effects of external heat flux and silicon doping were investigated. The predicted MD outputs showed high stability throughout the nanopumping process, even when different ratios of external heat flux were applied. The entropy value of the CNT-C20 system decreases from 412.91 to 403.394 eV/K as the heat flux increases to 0.03 W/m2. Also, the kinetic energy of the target atomic sample increased from 3.50 to 5.42 eV as heat flux increased. This kinetic energy enlarging occurred for the translational component of the target molecule’s kinetic energy, and the rotational component didn’t change effectively. Additionally, the results show that increasing atomic doping of silicon particles from 1 to 3 % decreased the displacement time of C20 molecule (7.22 ps for a 3 % doping ratio), indicating that atomic doping may also improve the nano-pumping process. By increasing Si doping to 3 %, the potential energy decreased, and the stability of the defined compound was reduced. This procedure caused the target molecule to not stabilize inside the nanotube sample, and this molecule displaced inside the deliverer system in less time. However, the negative ratio of potential energy showed physical stability of the total system wasn’t disrupted. With further doping increase to 5 %, the defined compound’s potential energy increased and stability enlarged. This process can be delayed nano-pumping procedure. Overall, the outcomes of this simulation provide insights into the optimal method for pumping fluids at the nanoscale and for drug delivery systems. These findings have practical implications for developing more efficient and effective drug delivery technologies that can help improve patient outcomes.

In this paper, the transport characteristics of two-dimensional systems has been investigated. Modeling by means of the Yukawa potential, in a wide range of values of the nonideality parameter, has been carried out. The Yukawa potential was chosen because of its wide applicability in the description of screened interactions in plasmas and other systems. A molecular dynamics method was used to determine the transport characteristics. The study was carried out with the aim of expanding the knowledge of heat transfer in two-dimensional systems. The paper presented the results of numerical experiments in which the dependences of the heat transfer and viscosity coefficients on the screening and non-ideality parameters in systems with Yukawa potential were studied. The obtained data can also serve as a basis for further theoretical and experimental studies in the field of transport characteristics of two-dimensional systems. These data not only expand the understanding of the peculiarities of two-dimensional systems, but also can be useful in the design and analysis of nanostructures and various microdevices. [ABSTRACT FROM AUTHOR]

This paper examines the satisfaction of the principle of corresponding states (PCS) on thepressure–density–temperature relation and the binary diffusion coefficient of hydrogen/oxygen mixture modelled as binary Lennard–Jones (LJ) fluid especially in a supercritical region. The hydrogen/oxygen mixture properties were computed by molecular dynamics simulation and compared with simulation results for a nitrogen/oxygen mixture as well as while using the Peng–Robinson (PR) equation of state (EOS) for both mixture types and a mono-component LJ-EOS. The Fuller–Schettler–Giddings model with the PR-EOS and Takahashi's EOS were used for binary diffusion coefficient comparison. The pseudocritical point concept of a fluid mixture was applied for PCS reduction and PCS satisfaction was conducted over a wide temperature range above the pseudocritical pressure with changing hydrogen molar fraction. PCS satisfaction for hydrogen/oxygen mixture properties was confirmed at reduced temperature of 1.5 or above. At reduced temperature of 1.0 or below, the hydrogen/oxygen mixture properties disagree with those of the comparison mixture because phase separation occurs. We conclude that the properties of hydrogen/oxygen mixtures can be estimated using the pseudocritical point concept and the investigated EOSs based on the PCS in the supercritical region at reduced temperature of1.5 or above. [ABSTRACT FROM AUTHOR]

Beta-amyloid peptide (Aβ) plays an important role in the mechanism of neurodegeneration in Alzheimer's disease. A fragment of beta-Aβ(25–35) amyloid peptide with the sequence GSNKGAIIGLM is considered to be the functional domain of the amyloid Aβ peptide responsible for its neurotoxic properties and the biologically active Aβ region. Conformational analysis by the method of molecular mechanics of each peptide segment of the C-terminal part of the peptide revealed a limited number of the most probable conformations and clearly defined the forces stabilizing the structures. The results we obtained showed that the Aβ(25–35) peptide energetically preferentially adopts the a-helical conformation at the C-terminal octapeptide segment. The molecular dynamics method was used to model the intramolecular mobility pattern of the Aβ(25–35) peptide molecule. It is shown that in the low-energy conformations of the Aβ(25–35) peptide, the flexible structures in its N-terminal region were oriented differently with respect to the structures in the C-terminal part. [ABSTRACT FROM AUTHOR]

This study examines the mechanism of nonlinear supratransmission (NST), which involves the transfer of disturbance to discrete media at frequencies not supported by the structure. We considered a model crystal with A3B stoichiometry. The investigation was carried out using atomistic modeling through molecular dynamics. The interatomic interaction was determined by a potential obtained through the embedded atom method, which approximates the properties of the Pt3Al crystal. The effect of NST is an important property of many discrete structures. Its existence requires the discreteness and nonlinearity of the medium, as well as the presence of a forbidden zone in its spectrum. This work focuses on the differences in the NST effect due to the anisotropy of crystallographic directions. Three planes along which the disturbance caused by NST propagated were considered: (100), (110), and (111). It was found that the intensity of the disturbance along the (100) plane is an order of magnitude lower than for more densely packed directions. Differences in the shape of solitary waves depending on the propagation direction were shown. Moreover, all waves can be described by a single equation, being a solution of the discrete variational equations of macroscopic and microscopic displacements, with different parameters, emphasizing the unified nature of the waves and the contribution of crystal anisotropy to their properties. Studying the NST phenomenon is essential due to numerous applications of the latter, such as implications in information transmission and signal processing. Understanding how disturbances propagate in discrete media could lead to advancements in communication technologies, data storage, and signal amplification where the earlier mentioned ability to describe it with analytical equations is of particular importance. [ABSTRACT FROM AUTHOR]

The H2O–3-amino-1-propanol (3AP) system at 300 K was studied by molecular dynamics, graph theory, and Delaunay simplex methods. All the molecules were shown to be bound into a three-dimensional network of hydrogen bonds over the entire range of concentrations in the system. The characteristics of the networks and their concentration dependences were determined. The frequency at which the environment of molecules changes is discussed. The results were compared with those for mixed networks in aqueous solutions of 1,3-propanediol and monoethanolamine. [ABSTRACT FROM AUTHOR]

In this work, we further developed a new approach for modeling the processes of the self-assembly of complex molecular nanostructures using molecular dynamics methods; in particular, using a molecular dynamics manipulator. Previously, this approach was considered using the example of the self-assembly of a phenylalanine helical nanotube. Now, a new application of the algorithm has been developed for implementing a similar molecular dynamic self-assembly into helical structures of peptide nanotubes (PNTs) based on other peptide molecules—namely diphenylalanine (FF) molecules of different chirality L-FF and D-FF. In this work, helical nanotubes were assembled from linear sequences of FF molecules with these initially different chiralities. The chirality of the obtained nanotubes was calculated by various methods, including calculation by dipole moments. In addition, a statistical analysis of the results obtained was performed. A comparative analysis of the structures of nanotubes was also performed using the method of visual differential analysis. It was found that FF PNTs obtained by the MD self-assembly method form helical nanotubes of different chirality. The regimes that form nanotubes of right chirality D from initial L-FF dipeptides and nanotubes of left chirality L from D-FF dipeptides are revealed. This corresponds to the law of changing the sign of the chirality of molecular helical structures as the level of their hierarchical organization becomes more complicated. [ABSTRACT FROM AUTHOR]

Composite materials are gaining increasing attention from researchers worldwide due to their ability to offer tailored properties for various technical challenges. One of these promising fields is metal matrix composites, including carbon-reinforced metals and alloys. These materials allow for the reduction of density while simultaneously enhancing their functional properties. This study is focused on the Pt-CNT composite, its mechanical characteristics, and structural features under uniaxial deformation depending on temperature and mass fractions of carbon nanotube (CNT). The mechanical behavior of platinum reinforced with carbon nanotubes of diameters varying in the interval 6.62–16.55 Å under uniaxial tension and compression deformation has been studied by the molecular dynamics method. Simulations for tensile and compression deformations have been done for all specimens at different temperatures (viz. 300 K, 500 K, 700 K, 900 K, 1100 K, and 1500 K). The calculated mechanical characteristics allow us to conclude that, compared to pure platinum, the Young's modulus increased by about 60%. The results indicate that yield and tensile strength values decreases with increase in temperature for all simulation blocks. This increase was due to the inherent high axial rigidity of CNTs. In this work, these characteristics are calculated for the first time for Pt-CNT. It can be concluded that CNTs can be an effective reinforcing material for composites based on a metal matrix under tensile strain. [ABSTRACT FROM AUTHOR]

In this work, bimetallic Cu-Ag nanoparticles of five stoichiometric compositions of various sizes were studied by molecular dynamics method using a many body EAM potential. Regularities of the structure formation are established, their characteristic features are described. In particular, in compositions with 10, 70, and 90 at.% Cu content, after the melt cooling, typical fcc structures with intersecting atomic planes of the hcp phase are formed. In compositions of 30 and 50 at.% Cu, the fraction of identified phases does not exceed 20% of the total number of atoms. A tendency to the formation of a core-shell structure was revealed in the case of a high copper content, while in the case of a high silver content, a so-called onion structure is formed. Using the caloric curves of the potential term of the internal energy, the melting and crystallization temperatures were determined. It has been established that the concentration dependences of the melting temperature of bimetallic Cu-Ag nanoparticles have a minimum corresponding to the equiatomic composition for all sizes. For the crystallization temperature, both the concentration dependences and the size dependences are less pronounced, but the minimum value of the crystallization temperature also corresponds to the equiatomic composition for all sizes; with an increase in the size of bimetallic Cu-Ag nanoparticles, a slight increase in the crystallization temperature is observed.

The processes of melting and crystallization of bimetallic Pt- and Pd-based nanoparticles have been studied by the method of molecular dynamics. The possibility of obtaining stable nanoparticles containing 3000 and 4000 atoms in the temperature range from 500 K to 1600 K is established. The concept about the possibility of fixing the temperatures of starting and ending of the phase transition for melting and crystallization is confirmed which was put forward earlier for monometallic platinum and palladium nanoparticles. The analysis shows that during the cooling of Pd-Pt nanoparticles with an initially uniform distribution of components, formation of a mixed structure with a surface monolayer of Pd atoms is observed. The possibility of structural segregation in bimetallic Pd-Pt nanoparticles containing 3000 and 4000 atoms is shown. At the same time, these two sizes correspond to different scenarios. For bimetallic nanoparticles with 3000 atoms, local zones are mainly polyhedral, and for bimetallic nanoparticles containing 4000 atoms, formation of extended band structures is observed.

The melting of titanium nanoclusters Tin (n = 3599, 28725, 97045) with different heating rates (from 0,1 to and 10,0 TK/s) was studied by the molecular dynamics method. Molecular dynamics simulation was carried out using the LAMMPS program on a multiprocessor computer. A many-particle potential of interatomic interaction was used. The crystal structure of a titanium nanocluster upon heating passes into the liquid phase through the formation of a system of atoms (islands) with an ordered local environment near the melting point. The appearance of the latter is due to the non-equilibrium of the simulated heating process – the system does not have time to relax to an equilibrium state for a chosen temperature. The melting temperature was taken as the average value between the temperatures of the beginning and finishing of the phase transition process. The temperature of the beginning of melting corresponded to the state of completion of formation of individual islands. At the end of melting, the nanostructure is characterized by a completely disordered structure. It is noted that the melting temperature increases with the size of the nanoparticle and the rate of its heating. The limiting temperatures of the considered phase transition (at N → ∞) are significantly lower than the melting temperature of the bulk titanium.

This work studied bimetallic nanoparticles Ni@Ag and Ag@Ni with the total number of atoms 4000 by the molecular dynamics method using the tight-binding potential. The pattern of segregation and structural formation is established and its characteristics are described. Based on the analysis of the behavior of the calorie curves of the potential part of the internal energy, the melting and crystallization temperature was determined. The data obtained suggest that the processes of segregation in Ni@Ag and Ag@Ni nanoparticles are associated with the nanoparticle stability. The silver shell loses its stability above 900 K, while the nickel core remains solid and retains its structure. At the same time, in Ni675@Ag3325 nanoparticles the processes of the surface segregation of the nucleus atoms were less pronounced, whereas in Ag675@Ni3325 nanoparticles silver atoms actively segregated onto the surface of the nanoparticle. The features and fundamental differences in the processes of melting and crystallization of these nanosystems, as well as the temperature ranges of their stability, are analyzed. The relationship between the degree of intensity of segregation processes of nanoalloys during modeling and the stability of these systems is shown.

Context: The mechanical properties and deformation mechanisms of CoCrNi medium-entropy alloy are studied through molecular dynamics simulations. The effects of temperature and average grain size on the elastic modulus, Poisson's ratio, yield stress, and maximum flow stress are investigated. Methods: The constant pressure molecular dynamics method is used to calculate the elastic modulus and Poisson's ratio of the alloy at different temperatures and average grain sizes. Simple tension simulations are conducted to determine the yield stress and maximum flow stress as a function of average grain size. The study also analyzes the dislocation behavior near grain boundaries at different temperatures using molecular dynamics simulations. The Hall-Petch and inverse Hall-Petch relationships are employed to describe the grain size–dependent deformation behavior of the alloy. [ABSTRACT FROM AUTHOR]

To elucidate the impact mechanism of the interfacial characteristics of Calcium Silicate Hydrate gel (CSH)–Montmorillonite (MMT) at the nanoscale on the strength of cement-stabilized montmorillonite soil, this paper begins by examining the interfacial energy. Through Molecular Dynamics (MD) simulation methods, the energy at the MMT and CSH binding interface is quantitatively calculated, and the correlation between the interfacial energy and macroscopic strength is determined in conjunction with grey relational analysis. Finally, based on the characterization results from X-ray diffraction (XRD), the accuracy and sources of deviation in the MD simulation results are discussed. The study shows the CSH-MMT interfacial energy is composed of van der Waals forces, hydrogen bond energy, and electrostatic interactions, which are influenced by the migration of cations; there is a good consistency between the CSH-MMT interfacial energy and the unconfined compressive strength (UCS) of cement-stabilized soil (cemented soil), with the interfacial energy decreasing as the number of water molecules increases and first decreasing then increasing as the number of MMT layers grows; by adjusting the mix proportions, the magnitude of the CSH-MMT interfacial energy can be altered, thereby optimizing the strength of the cemented soil.

This paper presents the results of molecular dynamic modeling, revealing that inserting confined graphene layers into copper crystal reduces the thermal conductivity of the whole composite, and the coefficient of thermal conductivity κ decreases upon an increase in the number of graphene layers. The injection of one, two, and three layers of 15 nm graphene leads to a change in the coefficient of thermal conductivity from 380 W/(m·K) down to 205.9, 179.1, and 163.6 W/(m·K), respectively. Decreasing the length of graphene layers leads to a decrease in the density of defects on which heat is dissipated. With one, two, and three layers of 8 nm graphene, the coefficient of thermal conductivity of the composite is equal to 272.6, 246.8, and 240.8 W/(m·K), appropriately. Meanwhile the introduction of an infinite graphene layer results in the growth of κ to 414.2–803.3 W/(m·K).

Nowadays, core/shell structures due to very high thermal and electrical conductivity are taken into account in the manufacture of many industrial sensors and catalysis. Ni–Al core/shell structures are known as one of the most practical materials due to their high chemical stabilities at elevated temperatures. Since the evaluation of the mechanical properties of the industrial core/shell catalysts is crucial, identification of the mechanism responsible for their plastic deformation has been a challenging issue. Accordingly, in this study, the mechanical properties and plastic deformation process of Ni–Al core/shell structures were investigated using the molecular dynamics method. The results showed that due to the high-stress concentration in the Ni/Al interface, the crystalline defects including dislocations and stacking faults nucleate from this region. It was also observed that with increasing temperature, yield strength and elastic modulus of the samples decrease. On the other hand, increasing the temperature promotes the heat-activated mechanisms, which reduces the density of dislocations and stacking faults in the material. Consequently, the obstacles in the slip path of the dislocations as well as dislocation locks are reduced, weakening the mechanical properties of the samples.

The molecular dynamics method is applied to simulate the behavior of two-dimensional electron clusters of various shapes containing about 100 particles. The influence of a magnetic field on the effects of ordering and disordering (melting) in such clusters is studied. The field dependence of the rms displacements of particles in clusters is determined, and the trajectories of electron motion are found as functions of temperature and magnetic field. Ordering and disordering in clusters were fixed by the appearance of characteristic features in the rms displacements of electrons in the system. Hysteresis was observed in the field dependence of these displacements at a fixed temperature. The obtained data are compared with the results for root-mean-square displacements of electrons in a two-dimensional electronic infinite crystal. The qualitative agreement was found with these results; at the same time, the field dependence of root-mean-square displacements in an unbounded crystal is much weaker than in the clusters under study. The influence of the cluster shape on ordering transitions is studied, and it is found that the shape of a defect-free cluster does not affect the transition conditions. The distribution of electron velocities in clusters is studied for various magnetic fields. [ABSTRACT FROM AUTHOR]

A Monte Carlo (MC) and molecular dynamics (MD) coupling simulation scheme for sputtered particle transport was first proposed in this work. In this scheme, the MC method was utilized to model the free-flight process of sputtered atoms, while the MD model was adopted to simulate the collision between the sputtered atom and background gas atom so as to self-consistently calculate the post-collision velocity of the sputtered atom. The reliability of the MD collision model has been verified by comparing the computation results of the MD model and of an analytical model. This MC-MD coupling simulation scheme was used to investigate the influence of target-substrate distance on the transport characteristic parameters of sputtered Cu atoms during magnetron sputtering discharge. As the target-substrate distance increased from 30 to 150 mm, the peak energy of the incident energy distribution of deposited Cu atoms decreased from 2 to 1 eV due to the gradual thermalization of sputtered atoms. The distribution of differential deposition rate in unit solid angle firstly became more forward-peaked and then reversely approached the cosine distribution, which was agreed with the existing experimental observations. This work is expected to provide a more realistic simulation scheme for sputtered particle transport, which can be further combined with the MD simulation of sputtered film growth to explore the influence mechanism of process parameters on the properties of sputtered film. [ABSTRACT FROM AUTHOR]

Numerical simulation of the process of melting of aluminum nanoparticles is carried out with the use of the methods of molecular dynamics. It is established that the melting of aluminum particles depends on the potential of their interaction and on the type of the particle symmetry. Dependence of the melting temperature of aluminum nanoparticles on the size of the latter is investigated. [ABSTRACT FROM AUTHOR]

The article provides a comparative analysis of stresses associated with the crack tip in an anisotropic elastic medium with cubic crystalline symmetry of elastic properties under mixed loading conditions obtained by two fundamentally different approaches: atomistic simulations and continuum fracture mechanics methods. The atomistic modelling approach is premised on the application of the molecular dynamics (MD) method implemented in the open source code program Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). The continuum mechanics approach is based on the classical elasticity theory of anisotropic media, in which the mechanical fields associated with the crack tip are represented by the crack tip stress and displacement series expansions generalizing the well-known classical asymptotical presentation of M. Williams to the case of anisotropic media. Using the MD method, a large series of computations of the loading of monocrystalline copper and aluminum plates with a face-centered cubic crystal lattice weakened by a central crack applying the embedded atom potential (EAM) was implemented. MD modeling is aimed at determining the atomic stresses and strains near the crack tip. The computed atomic stresses were compared with the stress field determined by the continuum elasticity theory of anisotropic media for crystal lattices with cubic symmetry of elastic properties. A comparative analysis was carried out for the angular dependencies of the stress and strain tensor components at various selected distances from the crack tip for the entire range of mixed deformation forms starting from pure tensile loading and ending with forms close to pure transverse shear. It is ascertained that the crack tip fields determined on the basis of two fundamentally different approaches, precisely, discrete and continuum, are completely consistent with each other. It is established that mathematical methods of continuum fracture mechanics can be applied to describe stress, strain and displacement fields at the atomic level. [ABSTRACT FROM AUTHOR]

This study examines the mechanism of nonlinear supratransmission (NST), which involves the transfer of disturbance to discrete media at frequencies not supported by the structure. We considered a model crystal with A3B stoichiometry. The investigation was carried out using atomistic modeling through molecular dynamics. The interatomic interaction was determined by a potential obtained through the embedded atom method, which approximates the properties of the Pt3Al crystal. The effect of NST is an important property of many discrete structures. Its existence requires the discreteness and nonlinearity of the medium, as well as the presence of a forbidden zone in its spectrum. This work focuses on the differences in the NST effect due to the anisotropy of crystallographic directions. Three planes along which the disturbance caused by NST propagated were considered: (100), (110), and (111). It was found that the intensity of the disturbance along the (100) plane is an order of magnitude lower than for more densely packed directions. Differences in the shape of solitary waves depending on the propagation direction were shown. Moreover, all waves can be described by a single equation, being a solution of the discrete variational equations of macroscopic and microscopic displacements, with different parameters, emphasizing the unified nature of the waves and the contribution of crystal anisotropy to their properties. Studying the NST phenomenon is essential due to numerous applications of the latter, such as implications in information transmission and signal processing. Understanding how disturbances propagate in discrete media could lead to advancements in communication technologies, data storage, and signal amplification where the earlier mentioned ability to describe it with analytical equations is of particular importance.

Al-Cu Nanocomposites (NCs) are widely used in industrial applications for their high ductility, light weight, excellent thermal conductivity, and low-cost production. The mechanical properties and deformation mechanisms of Metal Matrix NCs (MMNCs) strongly depend on the matrix microstructure and the interface between the matrix and the second phase. The present study relies on Molecular Dynamics (MD) to investigate the effects of temperature on the mechanical properties and elastic and plastic behavior of the Al-Cu NC with single-crystal and polycrystalline matrices. The effects of heating on microstructural defects in the aluminum matrix and the Al/Cu interface were also addressed in the following. It was found that the density of defects such as dislocations and stacking fault areas are much higher in samples with polycrystalline matrices than those with single-crystal ones. Further, by triggering thermally activated mechanisms, increasing the temperature reduces the density of crystal defects. Heating also facilitates atomic migration and compromises the yield strength and the elastic modulus as a result of the increased energy of atoms in the grain boundaries and in the Al-Cu interface. The results showed that the flow stress decreased in all samples by increasing the temperature, making them less resistant to the plastic deformation.

Investigation of the structure of nanoclusters at different temperatures is an urgent task of modern materials science. This fact is due to the prospect of their application in the creation of materials with unique physical, mechanical, chemical and operational properties. Computer simulation was carried out by the method of classical molecular dynamics in the LAMMPS software package. To describe the interatomic interaction in the cluster, a modification of the Finnis-Sinclair many-body potential was used. The structure of titanium nanoclusters of various sizes has been studied. They are obtained at various cooling rates from the liquid state. An increase in the cooling rate leads to the formation of a subblock structure and an increase in the number of atoms with a disordered environment. They are due to the fact that high cooling rates impede the equilibrium process of rearrangement of the atomic structure with the formation of long-range order. No regions with an icosahedral structure were found. It is shown that the crystallization temperature and binding energy decrease with decreasing nanocluster size. An increase in the cooling rate increases the temperature difference between the start and end points of crystallization, respectively. The simulation results indicate a less pronounced dimensional dependence of the crystallization temperature – its estimated value for a macroscopic system (810K) is much lower than the value for bulk titanium (1940K).

In this work, of the structure formation was investigated using Au-Ag, Ti-Al, Ti-V bimetallic nanoparticles as the patterns. These bimetallic nanoparticles have different atomic size mismatches and different crystallization temperatures. A series of molecular dynamics experiments was carried out. Based on their results, the final configurations with the lowest energy were analyzed and the concentration dependences of the mixing energy were obtained. An analysis of the concentration dependences of the mixing energy makes it possible to predict the compositions and sizes of bimetallic nanoparticles, which can exhibit instability, such as for Ti-V bimetallic nanoparticles. The asymmetry of individual concentration dependences of the mixing energy is evidence of specific structural transformations characteristic for the given composition and size. It has been established that structural segregation is characteristic for Au-Ag, Ti-Al bimetallic nanoparticles and it is actively manifested at low concentrations of a more low-melting component. The competing phases in this case are fcc and hcp phases. In addition, for the average sizes considered in the article, the dependence of the crystallization temperature on the composition of bimetallic nanoparticles was investigated.

This work studied bimetallic Au-Co nanoparticles of three stoichiometric compositions of various sizes by the molecular dynamics method using the tight-binding potential. The regularities of structure formation are established, their characteristic features are described. In particular, in compositions with 50 at% and 75 at% Au content, multiple small nuclei of local icosahedral symmetry are formed. Crystalline phases prevail only in the Co -25 at% Au composition with an increase in the particle size. Compositions are revealed in which the internal symmetry of a nanoparticle is determined by the presence of one icosahedron or a superstructure of several icosahedrons. The concentration dependences of the mixing energy of a bimetallic Au-Co nanoparticle are calculated. It is shown that there are concentrations of compositions at which bimetallic nanoalloys can exhibit instability in a certain size range. Crystallization temperatures were determined using the caloric curves of the potential part of the internal energy. It was found that the crystallization temperature demonstrates a moderate or significant, depending on the composition as well as growth with an increase in the size of bimetallic Au-Co nanoparticles.

Abstract Reducing the dielectric constant and loss of cellulose insulation can make the electric field distribution uniform in oil‐paper insulation systems and decrease the heat generation in dielectric materials, thus ensuring a reliable transformer operation. To guide the experimental design from the molecular level, the fluctuation method was introduced into the molecular dynamics simulation to evaluate the static permittivity of cellulose insulation, εs. The correlation between the dynamics parameter mean square displacement (MSD) and dielectric loss induced by orientational polarization, was investigated. The simulation results and experimental values of five types of cellulose insulation were compared to verify the rationality of the proposed method. The results indicated that the simulation values of εs for five models were agreed well with the experimental values in terms of both the magnitude and the variation trend. The simulation time and permittivity of the surrounding medium εRF are two key parameters, which determine the accuracy of the simulation results of εs. Considering the convergence, 15 ns was chosen as the lower limit of simulation time. The reaction field approximation was adopted to calculate the dipole‐dipole interaction instead of true interaction, that is, εRF→∞. The MSD results reproduced the experimental trend in dielectric loss, indicating that the method can qualitatively predict the dielectric loss of cellulose insulation. Hence, these methods are sufficient to guide design experiments and provide a route to understand the mechanism of the change in dielectric properties at the molecular level.

Insulation failure due to electrical tree degradation is a challenge for epoxy resin (EP) operating in high electric field environments. To provide an experimental basis for the electrical tree inhibition method, we observed the inception times/voltages and growth rates of EP electrical trees at different ambient temperatures in real time using a micro-charge-coupled device, and proposed an in situ nondestructive observation method for obtaining the three-dimensional morphology of the EP electrical tree by fluorescence imaging. We also elucidated the influence mechanism of ambient temperatures on the growth characteristics of electrical trees by the molecular dynamics method. The results revealed that increasing the ambient temperature could increase the fractional free volume of a cross-linked EP system, resulting in increased charge carrier damage to the molecular chains, thus promoting the growth of EP electrical trees. [ABSTRACT FROM AUTHOR]

In this work, we further developed a new approach for modeling the processes of the self-assembly of complex molecular nanostructures using molecular dynamics methods; in particular, using a molecular dynamics manipulator. Previously, this approach was considered using the example of the self-assembly of a phenylalanine helical nanotube. Now, a new application of the algorithm has been developed for implementing a similar molecular dynamic self-assembly into helical structures of peptide nanotubes (PNTs) based on other peptide molecules—namely diphenylalanine (FF) molecules of different chirality L-FF and D-FF. In this work, helical nanotubes were assembled from linear sequences of FF molecules with these initially different chiralities. The chirality of the obtained nanotubes was calculated by various methods, including calculation by dipole moments. In addition, a statistical analysis of the results obtained was performed. A comparative analysis of the structures of nanotubes was also performed using the method of visual differential analysis. It was found that FF PNTs obtained by the MD self-assembly method form helical nanotubes of different chirality. The regimes that form nanotubes of right chirality D from initial L-FF dipeptides and nanotubes of left chirality L from D-FF dipeptides are revealed. This corresponds to the law of changing the sign of the chirality of molecular helical structures as the level of their hierarchical organization becomes more complicated.

Composite materials are gaining increasing attention from researchers worldwide due to their ability to offer tailored properties for various technical challenges. One of these promising fields is metal matrix composites, including carbon-reinforced metals and alloys. These materials allow for the reduction of density while simultaneously enhancing their functional properties. This study is focused on the Pt-CNT composite, its mechanical characteristics, and structural features under uniaxial deformation depending on temperature and mass fractions of carbon nanotube (CNT). The mechanical behavior of platinum reinforced with carbon nanotubes of diameters varying in the interval 6.62–16.55 Å under uniaxial tension and compression deformation has been studied by the molecular dynamics method. Simulations for tensile and compression deformations have been done for all specimens at different temperatures (viz. 300 K, 500 K, 700 K, 900 K, 1100 K, and 1500 K). The calculated mechanical characteristics allow us to conclude that, compared to pure platinum, the Young’s modulus increased by about 60%. The results indicate that yield and tensile strength values decreases with increase in temperature for all simulation blocks. This increase was due to the inherent high axial rigidity of CNTs. In this work, these characteristics are calculated for the first time for Pt-CNT. It can be concluded that CNTs can be an effective reinforcing material for composites based on a metal matrix under tensile strain.

In this paper, we propose and use a new approach for a relatively simple technique for conducting MD simulation (MDS) of various molecular nanostructures, determining the trajectory of the MD run and forming the final structure using external force actions. A molecular dynamics manipulator (MD manipulator) is a controlled MDS type. As an example, the applicability of the developed algorithm for assembling peptide nanotubes (PNT) from linear phenylalanine (F or Phe) chains of different chirality is presented. The most adequate regimes for the formation of nanotubes of right chirality D from the initial L-F and nanotubes of left chirality L of their initial dipeptides D-F modes were determined. We use the method of a mixed (vector–scalar) product of the vectors of the sequence of dipole moments of phenylalanine molecules located along the nanotube helix to calculate the magnitude and sign of chirality of self-assembled helical phenylalanine nanotubes, which shows the validity of the proposed approach. As result, all data obtained correspond to the regularity of the chirality sign change of the molecular structures with a hierarchical complication of their organization. [ABSTRACT FROM AUTHOR]

Abstract In recent years, there have been many cases of transformer failures caused by corrosive sulfides. At present, research mainly focuses on the single sulfide dibenzyl disulphide, but few research on multiple sulphur or the oil‐paper hybrid insulation. In this study, three typical sulfides dibenzyl disulfide, hexadecyl mercaptan and benzothiophene were selected to form seven sulfide‐oil‐paper models. Then relaxation calculations were carried out, and through molecular dynamics simulation, the synergistic effect of different sulfides on the properties of insulating paper and insulating oil was discussed. Results show that the coexistence of the three sulfides has the most severe weakening on the mechanical properties of cellulose, and it also causes great damage to hydrogen bonds. Hexadecyl mercaptan has a weaker effect on hydrogen bond destruction, but it will greatly aggravate the cellulose chain movement. The viscosity of insulating oil is generally increased by the influence of sulfide. Hexadecyl mercaptan is the main factor affecting the viscosity. Thiophene has little effect on the viscosity, ctive protection technology on sulphur corrosion.